(a) Field of the Invention
The invention relates to a fuse circuit, and particularly to a fuse circuit with low power consumption.
(b) Description of the Related Art
FIG. 1 shows a schematic diagram illustrating a traditional fuse circuit 100. As shown in FIG. 1, the fuse circuit 100 includes a voltage establishing module 110 and a latch 120. The voltage establishing module 110 establishes a voltage level on a node A according to the blown-off status of a fuse I1 and the latch 120 subsequently latches the voltage level of the node A and generates an output signal.
Generally, the blown-off status of the fuse I1 is decided during the initial setting of the fuse circuit 100. In other words, a user can decide whether the fuse I1 is to be blown off or not during the initial setting so that the fuse circuit 100 provides different outputs.
An initial setting signal PU inputted to a transistor P3 of the voltage establishing module 110 is shown in FIG. 1. The initial setting signal PU has a low voltage level during the initial setting interval and a high voltage level after the initial setting. Therefore, the transistor P3 (PMOS) is conductive during the initial setting and becomes an open circuit after the initial setting.
Since the resistance of a fuse is generally smaller than the equivalent impedance of the transistor P3, the voltage on the node A is decided by the status of the fuse. In other words, if the fuse I1 is not blown off during the initial setting, the fuse I1 forms a closed circuit with the reference voltage source Vss and therefore the voltage level on the node A is pushed down to Vss. On the other hand, if the fuse I1 is blown off during initial setting, the transistor P3 is connected to the reference voltage source Vdd and therefore the voltage level on the node A is raised up to Vdd.
The latch 120 then latches the voltage level of the node A for generating a corresponding output. The latch 120 includes an inverter, including transistors N1 and P1, and a feedback transistor P2. If the fuse I1 is not blown off, the fuse I1 makes the voltage level on the node A down to Vss, as shown in FIG. 1, so that the output is kept at the high voltage Vdd. Since the transistor P2 is now non-conductive, the voltage level on the node A is kept at Vss. If the fuse I1 is blown off and the initial setting signal PU is at the low voltage level, the voltage level on the node A is Vdd and the output of the latch 120 is corresponding to the low voltage level Vss. Since the transistor P2 is now conductive, the voltage level on the node A is kept at Vdd.
However, the above mentioned fuse circuit structure has various disadvantages. At first, if blowing off the fuse I1 is not necessary during the initial setting, then both the fuse I1 and the transistor P3 are now conductive and that means considerably large dc current flows through the voltage establishing module 110 and therefore the power consumption of the fuse circuit 100 is increased. Furthermore, if the fuse I1 is not completely blown off during the initial setting, leakage current flows through the fuse I1 and the transistor P2 during the normal operation of the fuse circuit 100 to result not only in the increase of the power consumption of the fuse circuit 100 but also in the failure of the initial setting.
To resolve the above mentioned problems, FIG. 2 shows a schematic diagram illustrating a fuse circuit 200 according to another prior art. As shown in FIG. 2, a transistor N2 (NMOS) is provided between the fuse I1 and the node A in the fuse circuit 200. During the initial setting, the transistor N2 forms an open circuit and thus no current flows through fuse I1 to thereby solve one of the problems mentioned in the above.
However, the structure of the fuse circuit 200 induces another problem. Since the fuse circuit 200 is generally implemented with considerably large quantities in integrated circuits (such as those implemented in DRAM), one additional transistor N2 is added for each fuse circuit 200 and thus the manufacturing cost is definitely increased. Furthermore, the fuse circuit 200 cannot solve the problem of the leakage current that flows through the fuse I1 that is incompletely blown off and the transistor P2.